In magnetic disk apparatuses such as hard disks, servo patterns are written as servo information indicating information about positions on a magnetic disk. In the magnetic disk apparatus, by reading servo information from these servo patterns, a magnetic head can be moved to a target track.
The process of writing servo patterns onto the magnetic disk is called servo writing and is generally executed in the production process for magnetic disk apparatuses. In the conventional art, servo patterns are written at predetermined intervals (track pitches) to form tracks shaped like concentric circles or a spiral-shaped track with respect to the rotation center of the magnetic disk.
However, the track pitch of servo patterns may vary due to the influence of disturbance experienced during servo writing. If variation of the track pitch is large, servo gain varies, so that accuracy in detecting the head position, that is, accuracy in positioning the head decreases, and thus a malfunction such as a read error is likely to occur. Accordingly, a technique for reducing the influence of variation in the track pitch is desired.